Hyperlipidemias such as hypercholesterolemia and elevated serum triglyceride levels are among the most potent risk factors in the causation of atherosclerosis, which is the build-up of fatty plaque deposits within the walls of blood vessels. For example, high levels of serum cholesterol bound to low density lipoprotein (LDL), intermediate density lipoprotein (IDL) or very low density lipoprotein (VLDL) are known to correlate strongly with the occurrence of atherosclerosis in humans. In particular, it is known that the higher the circulating levels of cholesterol in the form of LDL, IDL and VLDL cholesterol, and the higher the circulating levels of other lipids such as triglycerides, the more likely it is that cholesterol and lipids will be deposited within the blood vessel wall and cause or contribute to atherosclerosis.
In hypercholesterolemia, for example, the increase in the blood cholesterol level is associated mainly with a rise in the concentration of LDL, IDL and VLDL cholesterol. However, the specific causes of hypercholesterolemia are complicated and varied. At least one kind of hypercholesterolemia, known as familial hypercholesterolemia, is caused by a mutation in the gene for the LDL receptor that moves cholesterol out of the blood, primarily in the liver. Much more commonly, hypercholesterolemia has been associated with genetic factors and high dietary intake of saturated fatty acids and cholesterol, resulting in elevated blood cholesterol levels. High serum triglyceride levels have also been associated with high dietary intake of fatty acids.
Reduction of hyperlipidemia, including hypercholesterolemia, results in a delayed onset of atherosclerosis and a decrease in the progression of atherosclerosis, thus reducing the risk of coronary heart disease. Atherosclerosis, the major cause of most cardiovascular disorders, is a complex process involving the blood vessel wall, many different blood elements and the immune system. Recent evidence indicates that immune-related inflammation of the Th1 type is a major factor in the initiation, progression and manifestations of the disease. Down-regulation of the Th1 type immune response has been shown experimentally to prevent the development of, and/or cause regression of, atherosclerosis.
Some forms of hyperlipidemia, including hypercholesterolemia, are potentially partially reversible with current techniques of preventive management. Taking cholesterol-lowering drugs can result in a reduction in serum cholesterol, and other drugs may lower serum triglyceride levels. Dietary therapy is usually recommended for all patients with hyperlipidemia but the effect is often not sufficient to reduce risk optimally.